It's been a year since Starcraft II: Wings of Liberty, and what a year. Starcraft II is the definitive PC strategy game; it's multiplayer and massive community re-invigorating e-Sports in the west. Now, it's time for the first expansion pack. We've played two single player missions from the game, and talked at length to the games developers, writers and designers. What follows today are the main points from the presentations and playtests, along with detailed impressions of what we played. Over the coming days we'll have more news from our extensive interviews.

So here are the facts:

Starcraft II: Heart of the Swarm features Kerrigan as a hero character in nearly all of the missions. She's able to swap between four ability types. The first two shown include a Zerg style corruption form, and a Ghost style Spec Ops form

In single-player, you'll be able to upgrade every unit in the Zerg arsenal, eventually splitting each of them into brand new unit types.

Examples shown so far include Zerglings that can spawn immediately, or leap at their enemies like raptors, Banelings that split apart or turn their kills into minerals and gas, or Roaches that heal themselves with every kill, or can move when burrowed.

There will be new units in multiplayer for all the races, but Blizzard have yet to confirm what they'll be.

Kerrigan has a new haircut.

It's about timeā?¦ we got to meet the monstersā?¦

The Zerg make themselves at home.

'Heart of the Swarm,' says Sam Didier, Blizzard's art director 'is a big old monster movie. We want it to make you feel like you're in control of the swarm.' It takes place a little bit after the first game, where Kerrigan, the former Queen of Blades, now free from the Zerg influence, seems to be feeling a little homesick. She's reunited with her former allies, but with little memory of what happened to her as the Zerg figurehead. She's aided and abetted by two Zerg natives: Abathur, a kind of beetle-esque evolution/mutation master and the remnants of the swarm's memories of Kerrigan made flesh; Izsha. She seems nice.

Kerrigan has a lot on her plate. She's dealing with a come-down, and she's dealing with two races who want her dead. 'Kerrigan's used to having one third of the Koprulu sector's firepower at her fingertips,' laughs Dustin Browder. 'Now she doesn't.' Meanwhile, 'both the Protoss and the Terrans see her as their number one enemy.'

What we saw is from the early game, but not right from the start. Kerrigan is re-integrating with the Swarm, instructing Abathur to upgrade Roaches, Banelings and Zerglings, while Ischa instructs her in reuniting disparate zerg armies.

Seconds after this screenshot was taken, everything on this map exploded into a fine green mist.

The first mission we played takes place on Charr. A Zerg queen, separated from the hive mind, has begun to construct her own Swarm. She must be quelled. On Charr, there are over 100 pre-fertilised eggs that can be instantly hatched. If Kerrigan can claim 100, she can rip apart her enemy's base. What follows is a race; can the good Zerg out hatch the bad Zerg?

The mission is pretty easy for experienced Starcraft II players ' particularly when you've gathered the required eggs and are handed 100+ banelings and zerglings on a plate. It's a great, hilarious moment: select all, then attack move all the way into the enemy base.

Between missions the Zerg troops you've unlocked can be upgraded in a similar, but divergent path to the Terran forces from Wings of Liberty. Mutagen, earned for completing optional objectives, is spent on unit talents; for Zerglings that includes spawning broodlings when they die, or moving faster (speedlings!), from a choice of three. When enough points have been spent, you're given a choice of two upgraded super-units, but choosing one path will lock the second from you. Each of these have a unique look and feel; I adored the sharpened dorsal fin on the raptorling.

Single player includes the same variety of unit upgrades as Wings of Liberty did for the Terrans.

The list of upgrades shown include:

For the zergling:

Posthumous mitosis: spawn two broodlings.

Metabolic Boost: 33% movement speed boost.

Rapid genesis: instant spawning.

At bifurcation, Zergling options are:

the Swarmling ' hatches in group of three, third swarmling at no additional mineral cost.

Raptor: Leaps to close with enemy units and has 10 additional health-points.

Baneling upgrades are currently:

Viscous discharge: banelings slow movement speed

Centrifugal hooks: Baneling movement increased by 25%

Rupture: Baneling splash damage increased by 25%

At evolution, the Baneling options are:

The Splitterling: splits into two smaller banelings on death, split occurs twice.

The Gorgeling: Reduces killed units and structure to collectible resources.

Roach upgrades are currently:

Chitinous Plating: Roach gains one armour.

Bile ducts: Roach gains +2 damage

Organic carapace: roach gains +2 life regeneration

At evolution, the Roach evolves to:

The Prowler: can move while burrowed

The Leech: Gains 10 life per kill: up to +60 life and heals more rapidly when burrowed.

The second mission in the demo sees the Zerg facing down Protoss on a slippy slidey ice world. You're first sent down to the planet to investigate another errant queen, but discover she's been murdered by Protoss forces. Before they get the word out that Kerrigan is back, you have to shut down and destroy their communication towers ' against a fifteen minute countdown. Matters are complicated by two external factors; mighty snow storms that at first dangerous, but later, let you attack the Protoss with impunity as they hide from the cold behind their shields, and giant yetis. The giant yetis are cool.

Hot Roach on Yeti action.

Kerrigan is on-screen for both of these missions as a hero character, with some neat tricks. She has four pools of abilities to call from that are chosen between missions, two of which are playable today. The first is a Spec Ops pool of abilities including an area of effect stun and snipe. The second is a Zerg like 'Corruption' set, which includes the neat trick of immediately popping an enemy unit, which bursts into a pool of Broodlings. Totally overpowered, totally hilarious.

What Blizzard didn't show of Heart of the Swarm was revealing. No new units, no new multiplayer features, no new maps. These are all coming. During our conversations, Chris Sigaty, Starcraft II's lead producer pointed out that 'around half of Starcraft II players didn't really venture into the multiplayer' ' they're content to watch games online but just tinker with the campaign. This first reveal of what Heart of the Swarm will contain is for them.

And it looks like a fine continuation of Starcraft II. I have one misgiving. I can't wait to finish Starcraft II: Heart of the Swarm with an upgraded, customized, totally overpowered army. I'm just sad that it will sit alone in my single player game. I'd dearly love to take this army online in a non-competitive, non-ladder multiplayer game. Modders: this is your opportunity. Make it so.